NestJS OpenAPI

OpenAPI & Documentation

Swagger (OpenAPI)

• Automation: ALWAYS use the Nest CLI Plugin (@nestjs/swagger/plugin).
  • Benefit: Auto-generates @ApiProperty for DTOs and response types. Reduces boilerplate by 50%.
  • Config: nest-cli.json -> "plugins": ["@nestjs/swagger"].
• Versioning: Maintain separate Swagger docs for v1, v2 if breaking changes occur.

Response Documentation

• Strictness: Every controller method must have @ApiResponse({ status: 200, type: UserDto }).
• Generic Wrappers: Define ApiPaginatedResponse<T> decorators to document generic PageDto<T> returns properly (Swagger doesn't handle generics well by default).
  • Technique: Use ApiExtraModels + getSchemaPath() in the custom decorator to handle the generic T ref.

Advanced Patterns

• Polymorphism: Use @ApiExtraModels and getSchemaPath for oneOf/anyOf union types.
• File Uploads: Document multipart/form-data explicitly.
  • Decorator: @ApiConsumes('multipart/form-data').
  • Body: @ApiBody({ schema: { type: 'object', properties: { file: { type: 'string', format: 'binary' } } } }).
• Authentication: Specify granular security schemes per route/controller.
  • Types: @ApiBearerAuth() or @ApiSecurity('api-key') (Must match DocumentBuilder().addBearerAuth()).
• Enums: Force named enums for reusable schema references.
  • Code: @ApiProperty({ enum: MyEnum, enumName: 'MyEnum' }).

Operation Grouping

• Tags: Mandatory @ApiTags('domains') on every Controller to group endpoints logically.

• Multiple Docs: generate separate docs for different audiences (e.g. Public vs Internal).

  SwaggerModule.createDocument(app, config, { include: [PublicModule] }); // /api/docs
  SwaggerModule.createDocument(app, adminConfig, { include: [AdminModule] }); // /admin/docs
  

Self-Documentation

• Compodoc: Use @compodoc/compodoc to generate static documentation of the module graph, services, and dependencies.
  • Use Case: New developer onboarding and architectural review.

Advanced OpenAPI

• Polymorphism: Use @ApiExtraModels and getSchemaPath for oneOf/anyOf union types.
  • Pattern: Register generic/sub-types in controller, refer via schema $ref.
• File Uploads: Document multipart/form-data explicitly.
  • Decorator: @ApiConsumes('multipart/form-data').
  • Body: @ApiBody({ schema: { type: 'object', properties: { file: { type: 'string', format: 'binary' } } } }).
• Authentication: Specify granular security schemes per route/controller.
  • Types: @ApiBearerAuth() or @ApiSecurity('api-key'). Match setup in DocumentBuilder.
• Enums: Force named enums for reusable schema references.
  • Code: @ApiProperty({ enum: MyEnum, enumName: 'MyEnum' }).
• Grouping: Segregate public vs. internal docs.
  • Setup: SwaggerModule.createDocument(app, config, { include: [AdminModule] }).